The present invention relates to a tool for processing drilled holes.
More particularly, it relates to a tool which has a shaft which can be clamped into a drive element which serves to execute a forward stroke of the tool into a working position within the hole, a return stroke, and an at least rotating working motion of the tool, wires clamped at one end of the shaft between two support elements on the shaft and being sprung bowing away from the shaft in an arc shape and coated with a cutting medium, with one of the support elements is axially adjustable relative to the shaft.
In a tool of this type, two sleeves are fitted on a solid shaft; these sleeves surround the shaft, at a distance from one another, and into them are inserted, between shaft and sleeve, on the side facing each other, a large number of wires which are supported with their ends on the sleeves, are tensioned in an arc shape, and are coated with a cutting agent. The wires lie very close together, so that they fill out the whole circumference around the shaft and cannot be displaced towards one another in the circumferential direction at the support point. One of the sleeves can be axially adjusted relative to the shaft by means of a screw thread, so that the wires can be prestressed to a greater or lesser extent, producing more or less bowing-out from the shaft. The tool is inserted into the holes to be treated, and can then be used, for example, to remove particles of material protruding from a transverse hole into the drilled hole, by a rotating motion. Due to the necessary close coverage with wires over the circumference, the tool is relatively rigid, but can process drilled holes of different diameters only within a narrow tolerance range. In order to prevent the wires from being twisted or pulled out, the direction of drive must be continuously reversed during the processing. Moreover, as the tool is relatively large it is not possible to go below a lower diameter range of the hole to be treated. For technical and production reasons, this diameter is 8 mm in the known tool. One disadvantage is that replacing the wires in the case of damage, or when the cutting agent coating has been worn off, necessitates, the replacement of all the wires, even if some of them could still be usable.
Such tools, and other tools, are used for ultra-fine and most closely toleranced after-treatment of holes, in particular, in those cases where there are also transverse holes breaking into the drilled holes. In items of this nature, after the completion of a longitudinal hole into which, for example, a pump plunger of a fuel injection pump will later have to operate under very high pressures of e.g. 1,000 bar, and after completion of the transverse holes leading into this longitudinal hole, the longitudinal hole is microfinished by honing after the workpiece has been hardened. Following such processes burrs regularly occur, which protrude into the transverse hole and would lead to faults in the operation of the fuel injection pump. These burrs must be removed. This can be achieved with a burring tool, such as is known from DE-OS 3333499. This is effected by inserting a deburring tool from the outside through the transverse hole which removes the burrs at the junction between the transverse hole and the longitudinal hole. A further problem exists in that the breakthrough of the transverse hole into the longitudinal hole is not in a flat plane, so that the deburring tool removes varying amounts of material from different areas of the circumference; thus the desired sharp-edged transition from transverse hole to longitudinal hole is not ensured. This deburring also has the result that, in turn, a residue of burrs protrudes into the longitudinal hole. This would result in causing the high-precision pump plunger to seize in the longitudinal hole. For this reason, the remaining burrs must subsequently be removed, once again, without detriment the surface of the finished honed longitudinal hole. This removal of the residual burr, or of burrs which protrude into a hole in general, can be effected by means of a tool in accordance with the state of technology mentioned above, or else round brushes are used whose external circumference is accurately matched to the diameter of the longitudinal hole and which has nylon bristles with a cutting agent added. These round brushes have a diameter which is accurately matched to the diameter of the longitudinal hole, and when they are used for the first time they must be clamped over a defined length and aligned to prevent running out of true. A further disadvantage is that the brushes have only a relatively short life, since due to wear, the diameter reduction is possible only in a very narrow range. Brush material being welded on to the wall of the longitudinal hole can also occur. Subsequent cleaning of the longitudinal hole in turn means increased expense. If the round brushes are used with cutting oil, then such deposits are avoided, but the efficiency of the bristles is diminished due to lower rigidity with reducing contact pressure. Furthermore, for each drilled hole diameter, an matched brush must be used, so that in the machines providing the processing, different workpiece diameters present a problem.